From 43b5987e8b00482782df766d1b726404f4e4b2a9 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Mon, 5 Nov 2018 17:48:26 +0000
Subject: [PATCH] spawn :let ID = INIT :let ID = INIT ... { ... }

---
 TODO.md                           |  1 +
 packages/syntax/src/generators.js | 10 ++++++++++
 packages/syntax/src/index.js      |  1 +
 packages/syntax/src/parser.js     | 18 ++++++++++++++++--
 packages/syntax/src/plugin.js     | 10 ++++++++++
 packages/syntax/src/types.js      | 12 +++++++++---
 6 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/TODO.md b/TODO.md
index fff8a20..bb04014 100644
--- a/TODO.md
+++ b/TODO.md
@@ -5,6 +5,7 @@
  - [DONE] `spawn*` or similar - looks like `spawn on start { ... }` will do the trick
  - [DONE] activation
  - [DONE] remove ground dataspace syntax
+ - [DONE] `spawn :let childVal = parentCalculation { ... }`
 
  - `defer` statement
  - `define/query`
diff --git a/packages/syntax/src/generators.js b/packages/syntax/src/generators.js
index 40ec24c..c57c71b 100644
--- a/packages/syntax/src/generators.js
+++ b/packages/syntax/src/generators.js
@@ -32,6 +32,16 @@ export function SpawnStatement(node) {
     this.space();
     this.print(a, node);
   }
+  for (let i = 0; i < node.parentIds.length; i++) {
+    this.space();
+    this.token(":let");
+    this.space();
+    this.print(node.parentIds[i], node);
+    this.space();
+    this.token("=");
+    this.space();
+    this.print(node.parentInits[i], node);
+  }
   this.space();
   this.printBlock(node.bootProc);
 }
diff --git a/packages/syntax/src/index.js b/packages/syntax/src/index.js
index e069a6a..5f74427 100644
--- a/packages/syntax/src/index.js
+++ b/packages/syntax/src/index.js
@@ -89,6 +89,7 @@ Array.prototype.push.apply(Types.TYPES, Object.keys(Types.DEPRECATED_KEYS));
 //
 Types.getBindingIdentifiers.keys.EventHandlerEndpoint = ["captureIds"];
 Types.getBindingIdentifiers.keys.DuringStatement = ["captureIds"];
+Types.getBindingIdentifiers.keys.SpawnStatement = ["parentIds"];
 
 //---------------------------------------------------------------------------
 // (3) Install our modified parser in place of the core parser.
diff --git a/packages/syntax/src/parser.js b/packages/syntax/src/parser.js
index d5eb62a..8f27274 100644
--- a/packages/syntax/src/parser.js
+++ b/packages/syntax/src/parser.js
@@ -202,10 +202,24 @@ export default class SyndicateParser extends _original_Parser {
       node.name = this.parseExpression();
     }
     node.initialAssertions = [];
+    node.parentIds = [];
+    node.parentInits = [];
     while (this.match(tt.colon)) {
       this.next();
-      this.expectContextual("asserting");
-      node.initialAssertions.push(this.parseExpression());
+      if (this.isContextual("asserting")) {
+        this.next();
+        node.initialAssertions.push(this.parseExpression());
+      } else if (this.state.type === tt._let) {
+        this.next();
+        const id = this.parseBindingAtom();
+        this.checkLVal(id, true, undefined, "spawn :let declaration");
+        this.expect(tt.eq);
+        const init = this.parseMaybeAssign(false);
+        node.parentIds.push(id);
+        node.parentInits.push(init);
+      } else {
+        this.unexpected();
+      }
     }
     node.bootProc = this.parseSyntheticFunctionStatement();
     return this.finishNode(node, "SpawnStatement");
diff --git a/packages/syntax/src/plugin.js b/packages/syntax/src/plugin.js
index a3221f8..16e258c 100644
--- a/packages/syntax/src/plugin.js
+++ b/packages/syntax/src/plugin.js
@@ -348,6 +348,16 @@ export default declare((api, options) => {
               SEQ: t.arrayExpression(node.initialAssertions)
             }),
         }));
+        if (node.parentIds.length > 0) {
+          const stmts = [];
+          for (let i = 0; i < node.parentIds.length; i++) {
+            const id = node.parentIds[i];
+            const init = node.parentInits[i];
+            stmts.push(template(`const ID = INIT;`)({ ID: id, INIT: init }));
+          }
+          stmts.push(path.node);
+          path.replaceWith(t.blockStatement(stmts, []));
+        }
       },
 
       FieldDeclarationStatement(path, state) {
diff --git a/packages/syntax/src/types.js b/packages/syntax/src/types.js
index f452a64..9ce1cd4 100644
--- a/packages/syntax/src/types.js
+++ b/packages/syntax/src/types.js
@@ -25,9 +25,9 @@ import defineType, {
 } from "@babel/types/lib/definitions/utils";
 
 defineType("SpawnStatement", {
-  builder: ["name", "initialAssertions", "bootProc"],
-  visitor: ["name", "initialAssertions", "bootProc"],
-  aliases: ["Statement"],
+  builder: ["name", "initialAssertions", "parentIds", "parentInits", "bootProc"],
+  visitor: ["name", "initialAssertions", "parentIds", "parentInits", "bootProc"],
+  aliases: ["Statement", "Scopable"],
   fields: {
     name: {
       validate: assertNodeType("Expression"),
@@ -39,6 +39,12 @@ defineType("SpawnStatement", {
         assertEach(assertNodeType("Expression")),
       ),
     },
+    parentIds: {
+      validate: chain(assertValueType("array"), assertEach(assertNodeType("Identifier")),),
+    },
+    parentInits: {
+      validate: chain(assertValueType("array"), assertEach(assertNodeType("Expression")),),
+    },
     bootProc: {
       validate: assertNodeType("FunctionExpression"),
     },